Trouble shooting cable television systems is a very difficult endeavor because such systems and their associated electronics are spread diversly over a large geographical area. The majority of systems are one-way with signals originating at a headend and being transmitted to many extremities. Failure of any one component in the chain is never witnessed or acknowledged at the central operations point. A subscriber loss of service complaint, received via telephone, is normally the first notification of a malfunction. However, as reported by the subscriber, it is often very difficult to judge the nature of the problem. A report of "no picture" can be a symptom resulting from a problem as severe as a total CATV system outage to simply the failure of the subscriber's television set which has no bearing on the cable plant operation.
Once a complaint has been lodged in a system operations center, the technical staff is dispatched to drive the length of the cable system in question, stopping occasionally to determine whether the signal is present at that point or if the problem is further down the line. Many times, this trouble shooting technique involves knocking on doors and asking subscribers to view their television receivers to see if they have the same complaint. This is both inconvenient and troublesome to the subscribers, very time consuming and therefore costly to the cable operator.
In order to ensure the integrity of shielding and thus minimizing intolerable interference from sources outside the coaxial environment and to comply with regulatory agency rules, most operators of networks place a uniquely encoded signal within their network, the sole purpose of which is to test for unacceptable radiation from the network. Using a detecting device with known characteristics, the user of the detecting device may isolate the location of any area within the network which exceeds predetermined radiation levels. Leakage in excess of established limitations can be traced to a lack of shielding integrity which will allow equally reciprocal amounts of ingress and egress. In most instances, tolerable ingress must be much less than regulatory agency rules allow in order to avoid interference to desired signals from those outside the network.
In the ideal network, one should expect never to sense the radiation control signal. It is therefore obvious that the same signal which is placed on the coaxial network for purposes of radiation monitoring cannot also be used directly to assist the network operator to isolate the location of an amplifier/repeater station which is malfunctioning. However, this signal can be used as a pilot signal the level of which can be sensed by interface hardware physically mounted directly to the output port of an existing broadband network amplifier. Duplicating the use of an existing signal is of extreme importance to the network operator as no additional bandwidth is required for non-revenue purposes.